1. Field of the Invention
The present invention relates to a pipeline fitting such as a branch pipeline fitting for connecting a main pipeline into which liquid such as gas flows to a branch pipeline for transfer of the gas in the main pipeline to a site which requires the gas, and, more particularly, to a plug and a plugging machine for a pipe fitting which are intended to prevent leakage of gas after a branching operation for a pipeline, repairing operation for a pipeline, or the like is completed.
2. Description of the Prior Art
Nowadays, processed gas is used predominantly in most dwellings, buildings, and the like as heating fuel. Hence, many gas pipes are built underground in all cities and towns in a xe2x80x9cnetxe2x80x9d fashion, which transfer processed gas from a gas processing plant to the specific sites.
Such gas fuel is transferred to sites through branch pipeline fittings which are adapted to connect a main pipeline connected to a gas manufacturing plant and to branch pipelines connected to the specific site.
To supply gas fuel from a main pipeline to sites such as dwellings or buildings, branch pipelines are first laid underground, and then are connected to the main pipeline by mounting branch pipeline fittings therebetween.
This type of operation for connecting a main pipeline and a branch pipeline by means of a branch pipeline fitting while gas flows through the main pipeline is carried out as follows:
(1) A lower end of a branch pipeline fitting is welded to an outer surface of a main pipeline while being in contact therewith, and then the branch pipeline fitting is welded to a branch pipeline which is laid underground in advance.
(2) A tapping valve is attached to an upper end of the branch pipeline fitting. A perforation machine is attached to an upper end of the tapping valve. After the tapping valve is opened, a tapping unit of the perforation machine is downwardly moved to the main pipeline. The main pipeline is perforated by rotating the tapping unit of the perforation machine.
(3) After the tapping unit of the perforation machine and the cut portion of the main pipeline are raised into the perforation machine, the tapping valve is closed. Thereafter, the perforation machine is removed from the tapping valve.
(4) A plugging machine for mounting a plug is attached to the tapping valve so as to prevent leakage of gas. The tapping valve is then removed and a closing plate is connected to the upper end of the branch pipeline fitting.
In this way, the branch pipeline is safely connected to the main pipeline while gas flows through the pipeline.
When a pipeline needs to be repaired, the pipeline is closed at its upstream. Such an operation of closing a pipeline will now be described with reference to FIGS. 1 and 2.
(1) A pipeline fitting 2 is welded at its lower end to a pipeline 1, and a tapping valve 3 is attached to the pipeline fitting 2.
(2) After a perforation machine is mounted on the tapping valve 3, the tapping valve is opened. A tapping unit of the perforation machine is downwardly moved to the pipeline, and then rotated to form an opening in the pipeline.
(3) A tapping unit of a perforation machine and a cut portion of the pipeline 1 are raised into the perforation machine. Thereafter, the tapping valve 3 is closed, and the perforation machine is then removed from the tapping valve.
(4) A plugging machine is attached to the tapping valve, and a temporary plug is then provided in the pipeline through the perforated opening of the pipeline 1 to block the downstream flow of gas. Then, the downstream portion of the pipeline 1 is repaired, and the temporary plug is removed from the pipeline 1.
(5) A plug 4 is loaded into the plugging machine and then locked into the pipeline fitting 2 to prevent leakage of gas. The tapping valve 3 is removed, and a closing plate 5 is mounted on the pipeline fitting 2.
As described above, after the downstream portion of the pipeline is repaired while gas flows in an upstream section of the pipeline, gas leakage from the pipeline can be reliably prevented.
An example of a plug, which is adapted to be locked to a pipeline in order to prevent gas leakage from the pipeline after a branching operation or a repair operation of the pipeline, is disclosed in U.S. Pat. No. 4,058,142.
As shown in FIG. 2, the prior art plug 4 disclosed in the patent comprises a cylindrical body 4b having an annular sealing groove 4a formed at its circumferential surface, an O-ring 4c fitted in the annular sealing groove 4a of the cylindrical body 4b, an enlarged plate 4d locked in an annular locking groove 2a formed at an inner surface of a pipeline fitting 2, and an expanding device 4e connected to a plugging machine, which is adapted to expand the plate 4d and thus cause the plate to be fitted in the annular locking groove 2a by a plugging machine.
In the prior art plug for a pipeline fitting, since the expanding device 4e is left on the plug 4 even after the plug 4 is completely locked in the pipeline fitting 2, every plug must be provided with the expanding device 4e. With such an expanding device present, production cost of the plug is thus increased and the structure of the plug becomes complicated. Furthermore, the pipeline 2 is thus increased in its height owing to the expanding device.
In addition, since the plug 4 cannot be retracted at its enlarged plate 4d once the plug is expanded and then locked in the pipeline fitting 2, the plug 4 cannot be removed from the fitting even when the pipeline is required to be repaired. Consequently, another pipeline fitting 2 must be again mounted at another portion of the pipeline and then the above-described operation must be carried out.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a plug for pipeline fitting which is provided with an expanding device adapted to be removed after the plug is locked in a pipeline fitting, thereby achieving simplification of its structure, reduction of production cost and decrease in height.
It is another object of the present invention to provide a plug for a pipeline fitting which is adapted to be removed from a pipeline fitting whenever required after being locked to the pipeline fitting.
It is a further object of the present invention to provide a plugging machine for a pipeline fitting which is used to mount the plug in a pipeline fitting and remove the plug therefrom.
In order to accomplish the above object, the present invention provides a plug for a pipeline fitting comprising: a cylindrical body having at its circumferential surface an annular groove, which is formed at its upper surface with threaded holes to be engaged with by screws, and which is centrally formed at its upper surface with a circular recess; an O-ring fitted in the annular groove of the cylindrical body; an expanding plate having a circumferential edge to be inserted into an annular groove formed at an inner surface of the pipeline fitting, which is divided into a pair of semicircular plates and provided with a central opening having a minor axis in the direction of expansion of the expanding plate and a major axis in the direction perpendicular to the expansion direction, and which is provided with a plurality of elongated holes corresponding to the screws of the cylindrical body to allow the expanding plate to be coupled to the cylindrical body by the screws, the half semicircular plates being provided with pins such that the pins are symmetrical to each other with respect to a dividing line of the expanding plate; and an expanding device for causing the outer edge of the expanding plate to be inserted into the annular groove of the pipeline fitting, which comprises a lower disc inserted into the circular recess of the cylindrical body, an upper disc having a pair of curved elongated holes into which the pins of the expanding plate are inserted and which is adapted to move the pins received therein outwardly, an annular groove formed between the upper disc and the lower disc into which the inner edges of the half expanding plates of the expanding plate are inserted, and a connecting projection to be connected to the plugging machine.
In order to accomplish the above object, the present invention also provides a plugging machine for a pipeline fitting comprising: a housing attached to a tapping valve and having a central hole; an adapter to be connected to a connecting portion of a locking device of a plug to be mounted on the pipeline fitting; an elevating pipe having a central through hole, which has a lower end to be coupled to the adapter and an upper end having a bushing screwed therein and rotating means; sealing means disposed between the elevating pipe and the central hole of the housing; one or more guide bars mounted on the housing to guide movement of the elevating pipe; means for releasably holding the elevating pipe, which is moved up and down along the guide bars; a threaded rod having the threaded portion to be engaged with the bushing of the elevating pipe, which functions to move the elevating pipe up and down; and means for rotatably holding the threaded rod, which is coupled to upper ends of the guide bars.